Measurements for Global Trade (WMD 2020 Message from the BIPM and BIML Directors)

Measurement Techniques -     

Convergence of iterative methods based on Neumann series for composite materials: Theory and practice

Iterative fast Fourier transform methods are useful for calculating the fields in composite materials and their macroscopic response. By iterating back and forth until convergence, the differential constraints are satisfied in Fourier space and the constitutive law in real space. The methods correspond to series expansions of appropriate operators and to series expansions for the effective tensor as a function of the component moduli. It is shown that the singularity structure of this function can shed much light on the convergence properties of the iterative fast Fourier transform methods. We look at a model example of a square array of conducting square inclusions for which there is an exact formula for the effective conductivity (Obnosov). Theoretically, some of the methods converge when the inclusions have zero or even negative conductivity. However, the numerics do not always confirm this extended range of convergence and show that accuracy is lost after relatively few iterations. There is little point in iterating beyond this. Accuracy improves when the grid size is reduced, showing that the discrepancy is linked to the discretization. Finally, it is shown that none of the 3 iterative schemes investigated overperforms the others for all possible microstructures and all contrasts.     

Antimicrobial Microwebs of DNA–Histone Inspired from Neutrophil Extracellular Traps

Neutrophil extracellular traps (NETs) are decondensed chromatin networks released by neutrophils that can trap and kill pathogens but can also paradoxically promote biofilms. The mechanism of NET functions remains ambiguous, at least in part, due to their complex and variable compositions. To unravel the antimicrobial performance of NETs, a minimalistic NET‐like synthetic structure, termed “microwebs,” is produced by the sonochemical complexation of DNA and histone. The prepared microwebs have structural similarity to NETs at the nanometer to micrometer dimensions but with well‐defined molecular compositions. Microwebs prepared with different DNA to histone ratios show that microwebs trap pathogenic Escherichia coli in a manner similar to NETs when the zeta potential of the microwebs is positive. The DNA nanofiber networks and the bactericidal histone constituting the microwebs inhibit the growth of E. coli. Moreover, microwebs work synergistically with colistin sulfate, a common and a last‐resort antibiotic, by targeting the cell envelope of pathogenic bacteria. The synthesis of microwebs enables mechanistic studies not possible with NETs, and it opens new possibilities for constructing biomimetic bacterial microenvironments to better understand and predict physiological pathogen responses.     

Tamil and English speech database for heartbeat estimation

The aim of this research work is to provide an open source database containing speech signals and the corresponding heartbeat rates, so as to further widen the area of research in speech signal processing, especially estimation of heartbeat rate from speech. Tamil and English Speech Database for Heartbeat Estimation consists of 10,040 speech recordings. The speech signals were recorded from 109 persons, 52 females and 57 males with an average age of 25 years and 6 months. The informed consented volunteers were asked to perform three tasks; like answering and reading in rest state; answering and reading after physical exercise and answering after watching video clips. 24-th and 72-nd order Mel-Frequency Cepstral Coefficients and 14-th and 52-nd order Auto Regressive Reflection Coefficients are extracted from the speech signal. Prediction of heartbeat is done by linear regression using support vector machine. The statistical significance of the heartbeat prediction results are improved by 10-fold speaker-independent cross validation scheme. Experimental results show a minimum average estimation error of ±?13.     

Effect of a new fermented soy milk product on serum lipid levels in normocholesterolemic adult men

This study was undertaken to verify the effect of a daily intake of a new fermented soy milk produced with Enterococcus faecium and Lactobacillus jugurti on the serum lipid levels in normocholesterolemic middle-aged men. The study was randomized, double-blind and placebo-controlled and was performed for a period of 6 weeks. Forty-four normocholesterolemic healthy, male volunteers, aged 40-55 years old were randomly separated in two groups: The F-group received 200 ml of the fermented product daily and the P-group received 200 ml of placebo (chemically fermented). The blood samples were drawn initially and after 3 and 6 weeks and serum values for total cholesterol, HDL-cholesterol and triglyceride were determined. The LDL-cholesterol value was estimated. No significant changes in the fermented group (F) were observed for total cholesterol, LDL-cholesterol or triglyceride levels, while the HDL-cholesterol level was significantly higher (p < or = 0.05) after 6 weeks. The total cholesterol and LDL-cholesterol levels were significantly higher (p < or = 0.05) in the placebo group (P), but no changes were found for the HDL-cholesterol and triglyceride levels during the experimental period. In conclusion, the intake of 200 ml/day of the fermented soy milk, produced with E. faecium and L. jugurti, for 6 weeks, did not affect the serum total cholesterol and LDL-cholesterol, and led an increase of 10% in the HDL-cholesterol level.     

Photocurable shape-memory polyether-polythioether/graphene nanocomposites and the study of their thermal conductivity

Herein a method is described to prepare photocurable thermally-conductive shape memory epoxy/ graphene composites. By photopolymerizing the epoxy resin diglycidyl ether of bisphenol A with an allyl-functionalized ditertiary amine as the curing agent, jointly with a multifunctional thiol, a crosslinked polyether-polythioether co-network was obtained. The presence of a soft domain like the flexible polythioethers enable the co-network to display shape memory properties. By varying the polyether to polythioether ratio it was possible to modulate the shape memory characteristics of the composite. The effect of the concentration of graphene nanoplatelets (GNP) in the composite was also investigated. Shape memory performances revealed excellent values of shape recovery and shape fixity with maximums of 98 and 99% respectively. The temporary- shaped composites with higher concentration of polythioethers and GNP regained their permanent shapes in 2–3 s when heated above the programming temperature. The thermal conductivity in the composites reached 0.39 W/m°K for the composite with 15% w/w of GNP. The presence of the polythioethers in the co-network enhanced the toughness of the composite as revealed by the impact resistance analysis.     

Slot coating flows of non‐colloidal particle suspensions

Slot coating is used in the manufacturing of functional films, which rely on specific particle microstructure to achieve the desired performance. Final structure on the coated film is strongly dependent on the suspension flow during the deposition of the coating liquid and on the subsequent drying process. Fundamental understanding on how particles are distributed in the coated layer enables optimization of the process and quality of the produced films. The complex coating flow leads to shear‐induced particle migration and non‐uniform particle distribution. We study slot coating flow of non‐colloidal suspensions by solving the mass and momentum conservation equations coupled with a particle transport equation using the Galerkin/Finite element method. The results show that particle distribution in the coating bead and in the coated layer is non‐uniform and is strongly dependent on the imposed flow rate (wet thickness). © 2016 American Institute of Chemical Engineers AIChE J, 63: 1122–1131, 2017     

Cover Image,Volume 66, Issue 10

The cover image, by Bruna A. Bregadiolli et al., is based on the Research Article Towards the synthesis of poly(azafulleroid)s: main chain fullerene oligomers for organic photovoltaic devices, DOI: 10.1002/pi.5419 .

     

Effect of watershed parameters on mercury distribution in different environmental compartments in the Mobile Alabama River Basin, USA

Total mercury (THg) and mono-methylmercury (MeHg) levels in water, sediment, and largemouth bass (LMB) (Micropterus salmoides) were investigated at 52 sites draining contrasting land use/land cover and habitat types within the Mobile Alabama River Basin (MARB). Aqueous THg was positively associated with iron-rich suspended particles and highest in catchments impacted by agriculture. Sediment THg was positively associated with sediment organic mater and iron content, with the highest levels observed in smaller catchments influenced by wetlands, followed by those impacted by agriculture or mixed forest, agriculture, and wetlands. The lowest sediment THg levels were observed in main river channels, except for reaches impacted by coal mining. Sediment MeHg levels were a positive function of sediment THg and organic matter and aqueous nutrient levels. The highest levels occurred in agricultural catchments and those impacted by elevated sulfate levels associated with coal mining. Aqueous MeHg concentrations in main river channels were as high as those in smaller catchments impacted by agriculture or wetlands, suggesting these areas were sources to rivers. Elevated Hg levels in some LMB were observed across all types of land use and land cover, but factors such as shallow water depth, larger wetland catchment surface area, low aqueous potassium levels, and higher Chl a concentrations were associated with higher Hg burdens, particularly in the Coastal Plain province. It is suggested that the observed large variability in LMB Hg burdens is linked to fish displacement by anglers, differences in food web structure, and sediment biogeochemistry, with surficial sediment iron oxides buffering the flux of MeHg from sediments to deeper water pelagic food webs.     

Performance of “Agave lecheguilla” natural fiber in portland cement composites exposed to severe environment conditions

The main objective of the present research was to provide the housing alternatives to istle zone rural areas in México, which represent about 10% of the national territory. The proposed solution involved a sustainable portland cement-based composite material, reinforced with high tensile strength natural fibers of “Agave lecheguilla”.